To control the flight of a missile or other rocket-powered vehicle after launch, thrust vector control (TVC) vanes can be placed in the path of the rocket motor's exhaust plume to direct the exhaust and thereby control the direction of the thrust and the flight of the missile. But placing TVC vanes in the exhaust plume reduces the efficiency of the rocket motor, which in turn limits the missile's maximum range. Once the missile reaches an aerodynamic control velocity, however, external aerodynamic control surfaces or fins can be used to control the missile, and the control vanes can be removed from the exhaust plume to minimize or eliminate their effect on the rocket motor's efficiency and to maximize its range.
Once the missile reaches a velocity where the external aerodynamic control surfaces can control the missile, the TVC vanes can be removed from the exhaust plume to minimize their effect on the rocket motor's efficiency, thereby increasing the missile's range. The TVC vanes can be removed from the exhaust plume using (1) dissolvable TVC vanes that erode in the rocket plume, or (2) retractable TVC vanes that can be moved out of the path of the rocket plume, or both. A dissolvable thrust vector control vane is disclosed in U.S. Pat. No. 6,548,794, for example, the entire disclosure of which is hereby incorporated herein by reference. Once the missile reaches the aerodynamic control velocity, the vanes dissolve in the exhaust plume, thereby removing their effect on the rocket motor's efficiency. These dissolvable control vanes require a specific type of solid propellant rocket motor, however, specifically a two-stage motor that changes from a non-corrosive propellant to a corrosive propellant, to quickly and effectively erode all the vanes simultaneously.
An example of a retractable TVC vane is disclosed in U.S. Pat. No. 5,320,304, which also is incorporated herein by reference in its entirely. The '304 patent discloses an integrated aerodynamic fin and stowable thrust vector reaction steering system, where each TVC vane can be retracted into a hollow space inside a corresponding aerodynamic fin. An extension and retraction linkage and an actuator for each vane are used to insert the vane into the rocket exhaust plume and then withdraw it after the missile reaches an aerodynamic control velocity. The control system for the aerodynamic fins also controls the attitude of the vane in the exhaust plume. For control, the aerodynamic fins rotate about an axis that generally is perpendicular to the longitudinal axis of the missile. The vanes, however, are spaced from that axis. Consequently, control schemes for these vanes must take into account a lateral translation of the vanes that accompanies a change in attitude.
In addition, the extreme environment of a rocket motor exhaust plume means that the TVC vanes often must be made of rare and expensive materials. For a solid propellant rocket, for example, the TVC vanes can be exposed to a 4000+ degree Fahrenheit (2200+ degree Celsius) rocket plume.